Thermostatic valves of the general type of this invention are well known and have been used in automotive cooling systems, for instance, for years. For example, see the U.S. Pat. Nos. 2,172,602; 2,356,958; 2,926,853; 2,981,477; 2,777,638 and 2,881,616 to Drapeau, C. D. Bailey, Obermair, Drapeau, Von Wangenheim, Wood, Salmon, Clifford and C. S. Bailey respectively as generally illustrative of this type of control valve.
Known thermostat control valves employ a thermal element or actuator such as that described in U.S. Pat. No. 2,368,181 to Vernet, for instance, to open the valve against a return spring and to close the valve with the assistance of the return spring.
Because conventional and commercially acceptable valves generally have been and are presently formed of a number of expensive parts, the cost of parts and labor, as in most other areas of manufacture, have led to an industry-wide effort to simplify the assembly and installation of such thermostatic control valves. For instance, one such effort to overcome the disadvantages of conventional valves and lower the cost of manufacture and assembly is disclosed in U.S. Pat. No. 3,606,149, to Obermair, cited previously. Here, the patentee puts forward the concept of integrating the design of the flow control assembly with the cooling system fitting.
A disadvantage to this approach from a commercial standpoint is the fact such an integrated structure cannot be used as a replacement for conventional valves already in use. Also the conduit itself must be specially fabricated and the over-all cost and number of parts of the complete assembly offers little, if any, competitive price advantage over the prior art. Further Obermair's patented structure suffers from the same flow efficiency reducing characteristic as those valves disclosed in the aforementioned patents--namely, a relatively wide, large fluid flow impeding bridge structure for securing the stem of a thermal actuator.
Compare this with the large surface area of resistance to fluid flow in the multi-legged spider type bridge shown in U.S. Pat. No. 2,829,834 to Drapeau and the flat and/or curved strap type bridges in U.S. Pat. Nos. 2,777,638 and 2,356,958 to Wood and Von Wangenheim respectively.
Present bridge structure is generally dictated by the strength required of the bridge to support the end of the stem of the thermal actuator permitting movement of the housing relative to the stem to open and close the valve. In engine cooling systems in which a thermostatic valve is installed on the outlet side of the engine between the engine and radiator the conventional bridge may be subjected to stem forces sufficient to push the stem through the bridge. This may also happen when the same thermostat is mounted in the engine inlet between the engine and conventionally a water pump the fluid pressure.
As is shown by the noted patents previous inventors have sought to meet these bridge strength requirements by providing a flat, wide strip, sometimes curved for greater strength or a multi and relatively wide legged spider. While these types of bridges often meet the necessary strength requirements, they have been found to impede rather than improve the fluid flow efficiency of the valve. This may be partially, if not totally, attributed to the fact that in conventional valves with the spider or strap bridge structure the fluid must flow against, out of and around the flow resisting surfaces of the bridge. The greater the surface area of resistance to flow, the more turbulence induced in the fluid as it streams through the valve opening and nozzle. It is believed this turbulent fluid flow may also affect the efficiency of the cooling system downstream of the valve as well.